How cold do temperatures need to be to trigger insect mortality?
There is no simple answer to this question. Mountain pine beetles overwinter primarily in their worm or grub stage (the larvae). During this time, they accumulate alcohols that act as an anti-freeze and provide protection from freezing. The beetles are more susceptible to cold temperatures early in the fall and late spring, when alcohol levels are low, and less susceptible to cold in mid-winter when alcohol levels are highest. Studies show that temperatures from -13 F to -31 F in mid-winter can cause mortality. However, factors such as the stage of development, duration of exposure to cold temperatures, responses to seasonal changes in temperatures, and geographical location will influence potential mortality. So what temperatures, at what time of the year, or for how long will cause extensive insect mortality is not yet well-understood.
